A method for recycling valuable metals in waste photovoltaic cells

Abstract

The present invention relates to a method for recovering valuable metals in waste photovoltaic cells, belonging to the technical field of recycling waste photovoltaic cells. The present invention adds waste photovoltaic silicon cells to excess alkaline solution for alkaline leaching, and separates the solid and liquid to obtain a solid phase and an alkaline leaching solution; the solid phase is a silver-containing silicon wafer and an aluminum hydroxide precipitate; the aluminum hydroxide precipitate is calcined to obtain aluminum oxide; the silver-containing silicon wafer is crushed and ground to obtain silver-containing silicon powder, the silver-containing silicon powder and the collector metal bismuth are mixed and heated under an argon atmosphere to melt the metal bismuth, and low-temperature bismuth captures silver under stirring conditions to obtain a silver-containing bismuth liquid, solid-liquid separation to obtain a bismuth-silver alloy and solid-phase silicon; the bismuth-silver alloy is heated under vacuum conditions and subjected to vacuum distillation separation to obtain metal bismuth and metal silver, and the metal bismuth is returned as a collector. The present invention can realize the recovery of valuable metals silver, silicon and aluminum in waste photovoltaic cells, and the process is simple and efficient.

Description

Technical Field

[0001] The invention relates to a method for recovering valuable metals in waste photovoltaic cells, belonging to the technical field of recycling waste photovoltaic cells. Background Art

[0002] Waste photovoltaic cells contain valuable metals such as silicon, silver, and aluminum. Recycling these valuable metals not only reduces ore mining and promotes resource sustainability, but also reduces energy consumption (compared to extracting metallic silicon, silver, and aluminum from ores, recycling these valuable metals from waste photovoltaic cells can reduce energy consumption by approximately 35% and CO2 emissions by 14%). Therefore, recovering valuable metals from waste photovoltaic cells can achieve sustainable development of photovoltaic energy.

[0003] Currently, the valuable metals in scrapped photovoltaic cells are primarily extracted using hydrometallurgical processes. This extraction process can be summarized as follows: first, acid is used to leach the scrapped photovoltaic silicon cells, dissolving the silver into a solution that is then filtered to obtain aluminum-containing silicon wafers. Alkali is then used to leach the aluminum-containing silicon wafers, converting the aluminum into aluminum hydroxide, and the solid silicon wafers are filtered and recovered. The silver that has entered the solution is subsequently subjected to multiple steps, including precipitation, oxidation, reduction, and electrolysis, using reagents such as acids, bases, hydrazine, organic solvents, and electrolytes, to produce high-purity silver. This complex and sophisticated hydrometallurgical process generates large amounts of wastewater that poses a potential threat to the environment, increasing wastewater treatment costs and the risk of environmental pollution. Summary of the Invention

[0004] In view of the problems of the existing technology in extracting valuable metals from waste photovoltaic cells, such as the complex process and large amount of waste liquid discharged, the present invention proposes a method for recovering valuable metals from waste photovoltaic cells. The waste photovoltaic silicon cells are pretreated with alkaline leaching to dissolve the aluminum on the waste photovoltaic silicon cells and convert them into aluminum hydroxide to obtain aluminum hydroxide powder and silver-containing silicon wafers. The aluminum hydroxide is calcined to obtain aluminum oxide. Bismuth metal is used as a capture agent to capture silver at low temperature (500-800°C) to obtain silver-containing bismuth liquid. At the capture temperature (500-800°C), the solubility of silicon (melting point 1414°C) in bismuth is extremely low (less than 0.5wt%). Therefore, during the capture process, silicon will remain in the solid phase. Since silicon (2.3g / cm 3 ) is much smaller than the density of bismuth (9.8 g / cm 3 ), silicon will float to the surface of the silver-containing bismuth liquid, and after solid-liquid separation, bismuth-silver alloy and solid-phase silicon will be obtained. Vacuum distillation of the bismuth-silver alloy can achieve the separation of metallic bismuth and metallic silver.

[0005] A method for recovering valuable metals from waste photovoltaic cells, comprising the following steps:

[0006] (1) adding waste photovoltaic silicon cells into excess alkaline solution for alkaline leaching to obtain a solid phase and an alkaline leaching solution; the solid phase is a silver-containing silicon cell and an aluminum hydroxide precipitate; the aluminum hydroxide precipitate is in a powdery state, and the aluminum hydroxide precipitate is calcined to obtain aluminum oxide;

[0007] (2) crushing and grinding the silver-containing silicon wafer to obtain silver-containing silicon powder, mixing the silver-containing silicon powder with a collector metal bismuth, and heating the mixture under an argon atmosphere to melt the metal bismuth. Under stirring conditions, the bismuth is trapped at low temperature to obtain a silver-containing bismuth liquid, and solid-liquid separation is performed to obtain a bismuth-silver alloy and solid-phase silicon.

[0008] (3) The bismuth-silver alloy is heated under vacuum conditions and subjected to vacuum distillation to separate metallic bismuth and metallic silver, and the metallic bismuth is returned to step (2) as a collector.

[0009] The alkali solution in step (1) is a NaOH solution or a KOH solution, and the concentration of the alkali solution is 5-10 mol / L.

[0010] The alkali leaching temperature in step (1) is 40-60° C. and the alkali leaching time is 10-25 minutes.

[0011] The calcination treatment temperature in step (1) is 1100-1300° C. and the calcination time is 2-4 hours.

[0012] The particle size of the silver-containing silicon powder in step (2) is 0.048-0.147 mm.

[0013] In the step (3), the mass ratio of the collector metal bismuth to the silver-containing silicon powder is 2:1 to 4:1, and the temperature at which the low-temperature bismuth captures silver is 500 to 800°C.

[0014] The vacuum degree of step (3) is 30-50 Pa, the temperature of vacuum distillation is 900-1100° C., and the time is 1-2 h.

[0015] The beneficial effects of the present invention are:

[0016] (1) The present invention can achieve efficient recovery of valuable metals silver, silicon and aluminum from waste photovoltaic cells;

[0017] (2) Compared with the hydrometallurgical recovery process, the silver recovery process of the present invention is greatly shortened (bismuth capture-vacuum distillation in two steps), and the discharge of waste liquid is greatly reduced; the shortening of the process flow can effectively reduce the recovery cost of valuable metals in waste photovoltaic cells and improve the recovery efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a process flow chart of the present invention;

[0019] Figure 2This is a graph showing the change of silver content in the silver-containing bismuth liquid with the number of capture times at different capture temperatures under different mass ratios of metallic bismuth and silver-containing silicon material;

[0020] Figure 3 This is a graph showing the change of silver content in the silver-containing bismuth liquid with capture temperature after capturing 10 batches of silver-containing silicon powder under different mass ratios of metallic bismuth and silver-containing silicon material. DETAILED DESCRIPTION

[0021] The present invention will be further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the contents described above.

[0022] Example 1: A method for recovering valuable metals from waste photovoltaic cells (see Figure 1 ), the specific steps are as follows:

[0023] (1) adding waste photovoltaic silicon cells to an excess alkali solution (10 mol / L NaOH solution) and leaching at 60° C. for 10 min, followed by solid-liquid separation to obtain a solid phase and an alkali leaching solution; the solid phase is a silver-containing silicon cell and an aluminum hydroxide precipitate; the aluminum hydroxide precipitate is in a powdery state, and the aluminum hydroxide precipitate is calcined at 1300° C. for 1 h to obtain aluminum oxide (with a purity of 97.7%);

[0024] (2) The silver-containing silicon wafer is crushed and ground to an average particle size of 0.147 mm to obtain silver-containing silicon powder. The silver-containing silicon powder and the collector metal bismuth are mixed and then heated in an argon atmosphere to melt the metal bismuth. The silver is then captured by low-temperature bismuth capture (low-temperature capture for 30 minutes) at a temperature of 500-800° C. under stirring to obtain a silver-containing bismuth liquid. The solid-liquid separation obtains a bismuth-silver alloy and solid-phase silicon. The mass ratio of the collector metal bismuth to the silver-containing silicon powder is 2:1. After 10 batches of silver-containing silicon powder are captured using the same bismuth liquid at a temperature of 800° C., the silver content in the silver-containing bismuth liquid is 4.5 wt.%, the average silver recovery rate is 98.7%, and the average purity of the solid-phase silicon is 99%. The change of the silver content in the silver-containing bismuth liquid with the number of captures at a temperature of 800° C. is shown in FIG. Figure 2 ,like Figure 2 As shown in FIG, after 2, 4, 6, and 8 captures, the silver contents are 0.87 wt.%, 1.83 wt.%, 2.66 wt.%, and 3.41 wt.%, respectively. Under the condition that the mass ratio of collector bismuth to silver-containing silicon material is 2:1, the silver content in the silver-containing bismuth liquid after 10 batches of silver-containing silicon powder are captured using the same bismuth liquid is changed with the capture temperature. Figure 3 At the capture temperatures of 500℃, 600℃, and 700℃, the silver contents in the silver-containing bismuth liquid were 4.16wt.%, 4.25wt.%, and 4.39wt.%, respectively;

[0025] (3) The bismuth-silver alloy was heated to 1100° C. under vacuum conditions and vacuum distilled at a vacuum of 50 Pa for 1 h to separate the metallic bismuth and metallic silver. The metallic bismuth was returned to step (2) as a collector. The silver purity in this embodiment was 99.7% (containing 0.15 wt % Si, 0.3 wt % Bi, and 0.05 wt % Sn).

[0026] Example 2: A method for recovering valuable metals from waste photovoltaic cells (see Figure 1 ), the specific steps are as follows:

[0027] (1) adding waste photovoltaic silicon cells to an excess of alkaline solution (5 mol / L NaOH solution) and leaching at 40° C. for 25 min, followed by solid-liquid separation to obtain a solid phase and an alkaline leaching solution; the solid phase is a silver-containing silicon cell and an aluminum hydroxide precipitate; the aluminum hydroxide precipitate is in a powdery state, and the aluminum hydroxide precipitate is calcined at 1100° C. for 2 h to obtain aluminum oxide (with a purity of 97.2%);

[0028] (2) The silver-containing silicon wafer is crushed and ground to an average particle size of 0.048 mm to obtain silver-containing silicon powder. The silver-containing silicon powder and the collector metal bismuth are mixed and then heated in an argon atmosphere to melt the metal bismuth. The silver is then captured by low-temperature bismuth at a temperature of 500-800° C. under stirring (low-temperature capture for 60 min) to obtain a silver-containing bismuth liquid. The solid-liquid separation obtains a bismuth-silver alloy and solid-phase silicon. The mass ratio of the collector metal bismuth to the silver-containing silicon powder is 4:1. After 10 batches of silver-containing silicon powder are captured using the same bismuth liquid at a temperature of 500° C., the silver content in the silver-containing bismuth liquid is 2.13 wt.%, the average silver recovery rate is 95.3%, and the average purity of the solid-phase silicon is 97.4%. The variation of the silver content in the silver-containing bismuth liquid with the number of captures at a temperature of 500° C. is shown in FIG. Figure 2 ,like Figure 2 As shown in FIG, after 2, 4, 6, and 8 captures, the silver contents are 0.45 wt.%, 0.84 wt.%, 1.29 wt.%, and 1.77 wt.%, respectively. Under the condition that the mass ratio of collector bismuth to silver-containing silicon material is 4:1, the silver content in the silver-containing bismuth liquid after 10 batches of silver-containing silicon powder are captured using the same bismuth liquid is changed with the capture temperature. Figure 3 At the capture temperatures of 600℃, 700℃, and 800℃, the silver contents in the silver-containing bismuth liquid were 2.2wt.%, 2.28wt.%, and 2.36wt.%, respectively;

[0029] (3) The bismuth-silver alloy was heated to 900° C. under vacuum conditions and vacuum distilled at a vacuum of 30 Pa for 2 h to separate the metallic bismuth and metallic silver. The metallic bismuth was returned to step (2) as a collector. The silver purity in this embodiment was 99.3% (containing 0.2 wt % Si, 0.4 wt % Bi, and 0.1 wt % Sn).

[0030] Example 3: A method for recovering valuable metals from waste photovoltaic cells (see Figure 1 ), the specific steps are as follows:

[0031] (1) adding waste photovoltaic silicon cells to an excess alkali solution (8 mol / L KOH solution) and leaching at 50° C. for 20 min, followed by solid-liquid separation to obtain a solid phase and an alkali leaching solution; the solid phase is a silver-containing silicon cell and an aluminum hydroxide precipitate; the aluminum hydroxide precipitate is in a powdery state, and the aluminum hydroxide precipitate is calcined at 1200° C. for 3 h to obtain aluminum oxide (with a purity of 97.4%);

[0032] (2) The silver-containing silicon wafer is crushed and ground to an average particle size of 0.074 mm to obtain silver-containing silicon powder. The silver-containing silicon powder and the collector metal bismuth are mixed and then heated in an argon atmosphere to melt the metal bismuth. The silver is then captured by low-temperature bismuth capture (low-temperature capture for 60 minutes) at a temperature of 700° C. under stirring conditions to obtain a silver-containing bismuth liquid. The solid-liquid separation obtains a bismuth-silver alloy and solid-phase silicon. The mass ratio of the collector metal bismuth to the silver-containing silicon powder is 3:1. After 10 batches of silver-containing silicon powder were captured using the same bismuth liquid at a temperature of 700° C., the silver content in the silver-containing bismuth liquid was 2.91 wt.%, the average silver recovery rate was 97.7%, and the purity of the solid-phase silicon was 98.3%.

[0033] (3) the bismuth-silver alloy is heated to 1000° C. under vacuum conditions and vacuum distilled for 2 h at a vacuum degree of 30 Pa to separate metallic bismuth and metallic silver, and the metallic bismuth is returned to step (2) as a collector;

[0034] The silver purity of this embodiment is 99.5% (containing 0.1 wt % Si, 0.3 wt % Bi, and 0.1 wt % Sn).

[0035] Example 4: A method for recovering valuable metals from waste photovoltaic cells (see Figure 1 ), the specific steps are as follows:

[0036] (1) adding waste photovoltaic silicon cells to an excess alkali solution (KOH solution with a concentration of 10 mol / L), alkali leaching is performed at a temperature of 50° C. for 15 minutes, and solid-liquid separation is performed to obtain a solid phase and an alkali leaching solution; the solid phase is a silver-containing silicon cell and an aluminum hydroxide precipitate; the aluminum hydroxide precipitate is in a powdery state, and the aluminum hydroxide precipitate is calcined at a temperature of 1200° C. for 4 hours to obtain aluminum oxide (purity of 97.6%);

[0037] (2) The silver-containing silicon wafer is crushed and ground to an average particle size of 0.061 mm to obtain silver-containing silicon powder. The silver-containing silicon powder and the collector metal bismuth are mixed and then heated in an argon atmosphere to melt the metal bismuth. The silver is then captured by low-temperature bismuth capture (low-temperature capture for 60 minutes) at a temperature of 700° C. under stirring conditions to obtain a silver-containing bismuth liquid. The solid-liquid separation obtains a bismuth-silver alloy and solid-phase silicon. The mass ratio of the collector metal bismuth to the silver-containing silicon powder is 4:1. After 10 batches of silver-containing silicon powder were captured using the same bismuth liquid at a temperature of 700° C., the silver content in the silver-containing bismuth liquid was 2.25 wt.%, the average silver recovery rate was 98.2%, and the purity of the solid-phase silicon was 98.7%.

[0038] (3) The bismuth-silver alloy was heated to 1100° C. under vacuum conditions and vacuum distilled at a vacuum of 50 Pa for 1 h to separate the metallic bismuth and metallic silver. The metallic bismuth was returned to step (2) as a collector. The silver purity in this embodiment was 99.2% (containing 0.1 wt % Si, 0.4 wt % Bi, and 0.2 wt % Sn).

[0039] The above describes the specific embodiments of the present invention in detail, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in this field without departing from the scope of the present invention.

Claims

1. A method for recovering valuable metals from waste photovoltaic cells, characterized in that: The specific steps are as follows: (1) Adding waste photovoltaic silicon cells into excess alkaline solution for alkaline leaching to obtain a solid phase and an alkaline leaching solution; the solid phase is a silver-containing silicon cell and aluminum hydroxide precipitate; the aluminum hydroxide precipitate is calcined to obtain aluminum oxide; (2) The silver-containing silicon wafer is crushed and ground to obtain silver-containing silicon powder, the silver-containing silicon powder and the collector metal bismuth are mixed and placed in an argon atmosphere for heating to melt the metal bismuth, and the low-temperature bismuth captures silver under stirring conditions to obtain a silver-containing bismuth liquid, and the solid-liquid separation is performed to obtain a bismuth-silver alloy and solid-phase silicon; the particle size of the silver-containing silicon powder is 0.048-0.147 mm, the mass ratio of the collector metal bismuth to the silver-containing silicon powder is 2:1-4:1, and the temperature for the low-temperature bismuth capture of silver is 500-800°C; (3) The bismuth-silver alloy is heated under vacuum conditions and subjected to vacuum distillation to separate metallic bismuth and metallic silver, and the metallic bismuth is returned to step (2) as a collector.

2. The method for recovering valuable metals from waste photovoltaic cells according to claim 1, characterized in that: The alkali solution in step (1) is a NaOH solution or a KOH solution, and the concentration of the alkali solution is 5-10 mol / L.

3. The method for recovering valuable metals from waste photovoltaic cells according to claim 1, characterized in that: The alkali leaching temperature in step (1) is 40-60°C and the alkali leaching time is 10-25 minutes.

4. The method for recovering valuable metals from waste photovoltaic cells according to claim 1, characterized in that: The calcination temperature in step (1) is 1100-1300° C. and the calcination time is 2-4 hours.

5. The method for recovering valuable metals from waste photovoltaic cells according to claim 1, characterized in that: In step (3), the vacuum degree is 30-50 Pa, the temperature of vacuum distillation is 900-1100° C., and the time is 1-2 h.

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